Hewitt argued that Trump must have familiarity with Duke given the former Ku Klux Klansman’s notoriety.

“I can’t imagine anybody who wants to be president not knowing who David Duke is,” he said. "[Trump] had denounced David Duke two days ago.”

Hewitt also noted that Trump pleading ignorance on Duke’s background recalls some of the greatest presidential campaign gaffes in American history.

“It’s like Mitt Romney’s ’47 percent’ moment,” he said, citing the 2012 GOP presidential nominee’s charge that at least “47 percent” of people would reelect President Obama because of their dependency on big government.

“It’s like Hillary Clinton saying she left the White House ‘impoverished,” he said. "It’s like Hillary Clinton saying she was named for [famed explored] Sir Edmund Hillary. She’s got a long list of these as well but none of them would be as devastating on election weekend in November as this one.”

Trump on Monday blamed a “lousy earpiece” for confusing an exchange with CNN anchor Jake Tapper over Duke’s backing the day before.